August 02, 2016

Isolated Woolly Mammoths Wiped Out By Pursuit Of Drink

Scientists have worked out what
killed off a side branch of woolly mammoths that survived 6000 years longer than
most of their species after they became ­marooned on a remote Alaskan island.

Researchers say mammoths
persisted for about 8000 years on St Paul Island, a chilly speck north of the
Aleutian Islands, after rising seas engulfed the land bridge between Siberia and
Alaska.

Quarantined from the stone- age
hunters who helped push mainland mammoths to extinction about 12,000 years ago,
the prehistoric beasts shared their windswept home with arctic foxes and shrews.
But they eventually drank themselves to death, trashing their island liferaft in
a desperate hunt for water.

The study, published in the
Proceedings of the National Academy of Sciences, offers a new explanation
for the demise of isolated mammoth populations in the Bering Strait.

The extinction of plant-­eating
megafauna elsewhere, including Australia, is usually blamed on the effects of
climate change, which ­reduced vegetation, and early hunters.

But the research team found no
evidence of human presence on the island until 1787, while the composition of
the vegetation remained “stable” during the ­period when the animals are thought
to have vanished.

Instead, the researchers ­believe
a drying phase in the ­climate concentrated the availability of drinking water
in a handful of lakes. This forced the animals to congregate nearby and strip
the surrounding areas of vegetation.

“Like elephants today, when the
water became cloudy and turgid, the mammoths probably dug holes nearby to obtain
cleaner water,” reported Penn State University, which led the study.

“Both of these things increased
erosion in the area and helped fill in the lake, decreasing the available water
even more.”

Mammoth remains found on the
island have been dated to about 6480 years ago, but other animals may have lived
more ­recently. The team analysed sediments from the bed of one of the lakes to
pinpoint when spores from fungi that grow on large animal dung had
disappeared.

The researchers also studied
“water isotope signatures” from the remains of aquatic organisms living in the
lake, and ­nitrogen isotopes from the bones of 14 newly discovered mammoth
skeletons.

All of them suggested
­progressively drying conditions.

“Multiple reinforcing lines of
evidence indicate that reduced freshwater availability triggered the extinction
of St Paul mammoths,” the paper says. They vanished 5600 years ago, give or take
a century, making their ­disappearance one of the “best-dated prehistoric
extinctions”.